Conventionally, there has existed a cooling construction for a voice coil type linear motor including a closed magnetic circuit formed into the θ-shape, by an inner yoke provided between a pair of outer yokes made up of magnetic materials arranged in parallel with a longitudinal center axis in such a manner as to be in parallel with the pair of outer yokes and side yokes provided at both end portions of the outer yokes and the inner yoke and permanent magnets provided on inner sides of the outer yokes and on outer sides of the inner yoke with polarities of the permanent magnets which face facing surfaces of the outer yoke and the inner yoke being made opposite, wherein an armature made up of a bobbin of non-magnetic and insulating materials and a coil provided around the bobbin is provided between the permanent magnets via air gaps in such a manner as to move in an axial direction, the cooling construction being characterized in that the bobbin is formed to have a cross section formed into the U-shape, whereby an interior of a cooler of a thin non-magnetic material is securely joined and fixed in place within a U-shaped groove and the coil is wound around an exterior of the cooler.
For example, according to JP-A-8-214530, a voice coil type linear motor such as shown in FIG. 5 is disclosed in order to provide a voice coil type linear motor which provides a good magnetic flux convergence, realizes a uniform magnetic flux flow through yokes, effects an effective operation of armature reaction over a whole stroke and saves space.
In FIG. 5, a field 50 is provided by a closed magnetic field formed into the θ-shape, by outer yokes 51, an inner yoke 52 and side yokes 53 and permanent magnets whose polarities are made opposite, and an armature 59 is provided via air gaps. The permanent magnets provided on the outer yokes 51 are made up of a plurality of permanent magnets 55a in which polarities of the adjacent permanent magnets are made opposite and which has the same width, the permanents magnets provided on the inner yoke 52 are made up of a plurality of permanent magnets 55b in which polarities of the adjacent permanent magnets are made opposite and which has the same width, and those of the permanent magnets which face each other are arranged in such a manner that the polarities thereof become different. Then, the coil is made up of a series coil 58a which divided at an equal pitch to that of the permanent magnets 55a and in which winding directions of the adjacent coils are made opposite, a thrust plate 58 having a flange 56 bent in a direction normal to the axial direction is fixed to sides and axial end portions of a bobbin 57, and work is connected to the flanges 56. Then, a cooler is provided in which a coolant is caused to flow through a magnetic gap between the inner yoke 52 and the bobbin 57 for cooling the coil.
In addition, a voice coil type linear motor is disclosed in JP-A-2002-27724 which has a cooling construction in which non-magnetic fluid cooled pipes which are formed into an integral unit by being bent in three dimensions or connected to each other in a watertight fashion are embedded in both surfaces which are defined between a coil and a cover on a non-magnetic gap side in such a manner as to extend from a fluid supply port to a fluid discharge port. According to the same unexamined patent publication, by provided a voice coil type linear motor having a construction such as shown in FIG. 6, a cooling function can be obtained which is free from a reduction in thrust and which can provide a high cooling performance and a high water tightness. In FIG. 6, a closed magnetic circuit is made up of an inner yoke 62, outer yokes 61 and side yokes 63, permanent magnets 65a, 65b are disposed on outer sides of the inner yoke 62 and inner sides of the outer yokes 61, and an armature 70 in which a coil 68 is wound around a bobbin is provided between the permanent magnets 65a, 65b via magnetic gaps. Then, a cover 69 which holds the armatures 70 and covers the respective yokes 61, 62, 63 and fluid cooled pipes 71 which are mounted between surfaces which are defined by the respective yokes 61, 62, 63 and the cover 69 which face each other in such a manner as to extend along an interior of the cover 69 are provided, and the fluid cooled pipes 71 are such as to be formed into an integral unit by bending a pipe line reaching from a fluid supply port 71A to a fluid discharge port 71B in three dimensions.
Incidentally, in the related arts, since the cooler exists on the magnetic gap side, the magnetic gap needs to formed wider, and in order to secure the thrust, an increase in current or the number of turns results, posing a problem of heat loss.
In addition, since the pipes and the bobbin are interposed between the coil making up a heat generating portion and the cooling medium, sufficient cooling effect could not be obtained.